Apparatus and methods of testing and assembling bumped devices using an anisotropically conductive layer

ABSTRACT

The present invention is directed toward apparatus and methods of testing and assembling bumped die and bumped devices using an anisotropically conductive layer. In one embodiment, a semiconductor device comprises a bumped device having a plurality of conductive bumps formed thereon, a substrate having a plurality of contact pads distributed thereon and approximately aligned with the plurality of conductive bumps, and an anisotropically conductive layer disposed between and mechanically coupled to the bumped device and to the substrate. The anisotropically conductive layer electrically couples each of the conductive bumps with a corresponding one of the contact pads. In another embodiment, an apparatus for testing a bumped device having a plurality of conductive bumps includes a substrate having a plurality of contact pads distributed thereon and substantially alignable with the plurality of conductive bumps, and an anisotropically conductive layer disposed on the first surface and engageable with the plurality of conductive bumps to electrically couple each of the conductive bumps with a corresponding one of the contact pads. Alternately, the test apparatus may also include an alignment device or a bumped device handler. In another embodiment, a method of testing a bumped device includes engaging a plurality of contact pads with an anisotropically conductive layer, engaging the plurality of conductive bumps with the anisotropically conductive layer substantially opposite from and in approximate alignment with the plurality of contact pads, forming a plurality of conductive paths through the anisotropically conductive layer so that each of the conductive bumps is electrically coupled to one of the contact pads, and applying test signals through at least some of the contact pads and the conductive paths to at least some of the conductive bumps.

TECHNICAL FIELD

The present invention relates to apparatus and methods of testing andassembling bumped die and bumped devices using an anisotropicallyconductive layer, suitable for testing, for example, flip chip die, chipscale packages, multi-chip modules, and the like.

BACKGROUND OF THE INVENTION

Bumped die and other bumped devices are widely used throughout theelectronics industry. As the drive toward smaller electronics continues,the pitch (or spacing) of solder bumps on such bumped devices continuesto decrease. The increasingly finer pitches of the solder bumps onbumped die and bumped devices raise concerns about the reliability ofthese devices. These concerns are being addressed by testing.

A die (or chip) is typically tested during the manufacturing process toensure that the die conforms to operational specifications. Solder bumps(or balls) are then formed on bond pads of the die using a solderdeposition device, such as a solder ball bumper. The solder bumps aretypically formed with a height of from 25 μm to 75 μm. The bumped dieare then tested by placing conductive test leads in contact with thesolder bumps on the die, applying a test signal to the bumps via thetest leads, and determining whether the bumped die responds with theproper output signals. If the bumped die tests successfully, it may beinstalled on a printed circuit board, a chip scale package, asemiconductor module, or other electronics device.

FIG. 1 is a cross-sectional view of a bumped die 10 engaged with a testcarrier 20 in accordance with the prior art. In this typicalarrangement, the bumped die 10 includes a substrate 12 with a pluralityof bond pads 14 thereon. A solder bump 16 (or other suitable conductivematerial) is formed on each of the bond pads 14. The test carrier 20 hasa plurality of contact pads 22 thereon, each of the contact pads 22being electrically coupled with a test lead 24. For testing of thebumped die 10, the solder bumps 16 engage the contact pads 22 of thetest carrier 20, and the appropriate test signals are applied to thebumped die 10 through some of the test leads 24. Output signals from thebumped die 10 are monitored through other test leads 24 to determinewhether the bumped die 10 is functioning to specifications. Test carrierapparatus of the type shown in FIG. 1 for testing unpackaged die aredescribed in U.S. Pat. No. 5,519,332 to Wood et. al., incorporatedherein by reference.

Testing of the bumped die 10 generally includes four levels of testing.A first or “standard probe” level includes the standard tests for grossfunctionality of die circuitry. A second or “speed probe” level includestesting the speed performance of the die for the fastest speed grades. Athird or “bum-in die” level involves thermal cycling tests intended todrive contaminants into the active circuitry and to detect earlyfailures. And a fourth or “known good die (KGD)” level includes testingto provide a reliability suitable for final products.

To ensure proper transmission of the test signals and output signals,the solder bumps 16 may be temporarily connected with the contact pads22 by reflowing the bumps, thereby soldering the bumps to the contactpads. After the testing is complete, the solder bumps 16 may be reflowedto disconnect the bumps from the contact pads. Connecting anddisconnecting the solder bumps 16 from the contact pads 22, however,involve time consuming processes and may damage the solder bumps 16 orthe contact pads 22.

Another problem with soldering the solder bumps 16 to the contact pads22 is that the coefficient of thermal expansion (CTE) of the bumped die10 may be appreciably different from the CTE of the test carrier 20.During burn-in die testing, the bumped die 10 and test carrier 20 areplaced in a burn-in oven and subjected to temperature cycling (e.g. −55°C. to 150° C.) for a time period of from several minutes to severalhours or more. Due to the different CTE of the bumped die 10 and thetest carrier 20 and the rigidity of the solder connections, significantstresses may develop throughout the components. These stresses mayresult in delamination or other damage to the bumped die 16 or the testcarrier 20, and may degrade or damage the connection between the solderbumps 16 and the bond pads 14.

An alternate approach to soldering is to simply compress the solderbumps 16 into engagement with the contact pads 22. Ideally, only a smallcompression force is needed to engage the solder balls 16 against thecontact pads 22 so that tests may be conducted. Methods and apparatusfor testing die in this manner are fully described in U.S. Pat. No.5,634,267 to Farnworth and Wood, incorporated herein by reference. Theapplied compression force, however, must be kept to a minimum becauselarger forces may damage the circuitry of the bumped die 10 or the testcarrier 20.

A problem common to both the solder reflow and the compression forcemethods of engagement is that the solder bumps 16 are not uniformlyshaped. As shown in FIG. 1, the solder bumps 16 are usually of differentheights. Using typical manufacturing methods and solders, the nominalvariation between the tallest and shortest bumps (shown as a distance don FIG. 1) is presently about 10% of the average solder ball height.Therefore, when the bumped die 10 is placed on the test carrier 20, theshorter solder bumps may not touch the corresponding contact pads. Insome cases, especially for very fine pitch solder bumps, the gapsbetween the shorter solder bumps and the contact pads may be too largeto overcome using solder reflow (because of the small volume of solderin each bump) or by using compression force (because of possible damageto the bumped die).

The variation in solder bump height also creates uncertainty in thefinal assembly of electronics components that include bumped devices. Asthe number of bumps on the bumped device increases, the failure rate ofthe assembled package increases due to solder bump non-uniformity.

FIG. 2 is a partial cross-sectional view of the bumped die 10 of FIG. 1engaged with another conventional test carrier 40. The test carrier 40includes a test substrate 42 having a plurality of pockets 44 disposedtherein. As shown in FIG. 2, the pockets 44 have sloping sidewalls 46,and a pair of contact blades 48 project from opposing sidewalls 46 intoeach pocket 44. Conductive test leads 50 are formed on the testsubstrate 42, including on the sidewalls 46 and contact blades 48 of thepockets 44.

During testing, the solder bumps 16 at least partially engage thepockets 44 of the test carrier 40 with the sharp contact blades 48partially penetrating the solder bumps 16. The solder bumps 16 may alsocontact the sloping sidewalls 46 of the test carrier 40. Thus, thedesired electrical connection between the solder bumps 16 and the testleads 50 may be achieved despite the variation in the solder bumpheight.

Although the test carrier 40 having pockets 44 with contact blades 48addresses solder bump height variation, testing solder bumps with thetest carrier 40 has several disadvantages. For example, because thecontact blades 48 penetrate the solder bumps 16, the solder bumps may becracked, chipped, or otherwise damaged by the contact blades. The solderbumps 16 may also become stuck to the contact blades 48, requiringadditional time and effort to disengage the bumped die 10 from the testcarrier 40. Furthermore, the test carrier 40 with the plurality ofpockets 44 is relatively costly to fabricate and more difficult tomaintain than alternative test carriers having flat contact pads.

FIG. 3 is a partial cross-sectional view of the bumped die 10 of FIG. 1engaged with another prior art test carrier 60. In this example, thetest carrier 60 includes a test substrate 62 having a plurality ofpedestals 64 formed thereon. Test leads 66 are disposed on the testsubstrate 62, each test lead 66 terminating in a contact pad 68 on thetop of each pedestal 64. A plurality of projections 69 project from eachcontact pad 68. Apparatus for testing semiconductor circuitry of thetype shown in FIG. 3 are more fully described in U.S. Pat. No. 5,326,428to Famworth et. aL, U.S. Pat. No. 5,419,807 to Akram and Famworth, andU.S. Pat. No. 5,483,741 to Akram et. al., which are incorporated hereinby reference.

To conduct a test of the bumped die 10, the solder bumps 16 engage thecontact pads 68 so that the sharp projections 69 at least partiallypenetrate the solder bumps 16. The projections 69 may be properly sizedto penetrate into the taller solder bumps, allowing the shorter solderbumps to at least contact the projections of the corresponding contactpad 68.

One of the drawbacks of testing bumped die using the carrier 60 havingprojections 69 is that the projections (like the contact blades 48described above) may damage the solder bumps 16. Furthermore, theprojections 69 are relatively expensive to manufacture, particularlywhen the projections must be sized to account for a nominal 10%variation in the solder bump height.

SUMMARY OF THE INVENTION

The present invention is directed toward apparatus and methods oftesting and assembling bumped devices using anisotropically conductivelayers. In one aspect of the invention, a semiconductor device comprisesa bumped device having a plurality of conductive bumps formed thereon, asubstrate having a plurality of contact pads distributed thereon andapproximately aligned with the plurality of conductive bumps, and ananisotropically conductive layer disposed between and mechanicallycoupled to the bumped device and to the substrate. The anisotropicallyconductive layer electrically couples each of the conductive bumps witha corresponding one of the contact pads, providing electrical contactbetween the conductive bumps and the contact pads despite variation inconductive bump height, and without damaging the conductive bumps.

In another aspect, an apparatus for testing a bumped device having aplurality of conductive bumps includes a substrate having a plurality ofcontact pads distributed thereon and substantially alignable with theplurality of conductive bumps, and an anisotropically conductive layerdisposed on the first surface and engageable with the plurality ofconductive bumps to electrically couple each of the conductive bumpswith a corresponding one of the contact pads. Alternately, the testapparatus may also include an alignment device. In another aspect, thetest apparatus may include a bumped device handler. The test apparatusprovides for rapid and efficient engagement, testing, and disengagementof the bumped device.

In another aspect of the invention, a method of forming a semiconductordevice includes providing a bumped device having a plurality ofconductive bumps formed thereon, providing a substrate having aplurality of contact pads distributed thereon, forming ananisotropically conductive layer between the conductive bumps and thecontact pads, approximately aligning the plurality of conductive bumpswith the plurality of contact pads, and engaging the plurality ofconductive bumps and the plurality of contact pads with theanisotropically conductive layer to electrically couple each of theconductive bumps with a corresponding one of the contact pads.

In yet another aspect of the invention, a method of testing a bumpeddevice includes engaging a plurality of contact pads with ananisotropically conductive layer, engaging the plurality of conductivebumps with the anisotropically conductive layer substantially oppositefrom and in approximate alignment with the plurality of contact pads,forming a plurality of conductive paths through the anisotropicallyconductive layer so that each of the conductive bumps is electricallycoupled to one of the contact pads, and applying test signals through atleast some of the contact pads and the conductive paths to at least someof the conductive bumps. Alternately, the method further includes atleast partially curing the anisotropically conductive layer. The methodadvantageously reduces the time, effort and expense involved inconnecting and disconnecting the conductive bumps from the contact pads,reduces the potential for damage to the conductive bumps or the contactpads, and accommodates variation in the heights of the conductive bumps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a bumped die engaged with a testcarrier in accordance with the prior art.

FIG. 2 is a partial cross-sectional view of the bumped die of FIG. 1engaged with an alternate embodiment of a test carrier in accordancewith the prior art.

FIG. 3 is a partial cross-sectional view of the bumped die of FIG. 1engaged with another embodiment of a test carrier in accordance with theprior art.

FIG. 4 is a partial cross-sectional view of the bumped die of FIG. 1engaged with a test carrier in accordance with an embodiment of theinvention.

FIG. 5 is a partial cross-sectional view of the bumped die of FIG. 1engaged with a test carrier in accordance with an alternate embodimentofthe invention.

FIG. 6 is a partial cross-sectional view of the bumped die of FIG. 1engaged with a test carrier in accordance with another alternateembodiment of the invention.

FIG. 7 is a partial cross-sectional view of the bumped die of FIG. 1engaged with a test carrier in accordance with yet another embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is generally directed toward apparatus andmethods of testing and assembling bumped die and bumped devices usinganisotropically conductive layers. Many specific details of certainembodiments of the invention are set forth in the following descriptionand in FIGS. 2-7 to provide a thorough understanding of suchembodiments. One skilled in the art, however, will understand that thepresent invention may have additional embodiments, or that the presentinvention may be practiced without several of the details described inthe following description.

Throughout the following discussion, apparatus and methods in accordancewith the invention are described in relation to the testing and assemblyof bumped die. It is understood, however, that the inventive apparatusand methods may be used to test and assemble any number of bumpeddevices, including chip scale packages, chip modules, or any otherbumped devices. To simplify the following discussion, however, theinventive apparatus and methods are described in relation to testing andassembly of bumped die with a test carrier or a printed circuit board,allowing the reader to focus on the inventive aspects.

FIG. 4 is a partial cross-sectional view of the bumped die 10 of FIG. 1engaged with a test carrier 100 in accordance with an embodiment of theinvention. In this embodiment, the test carrier 100 includes a testsubstrate 102 having a plurality of contact pads 104 coupled with aplurality of test leads 106. An anisotropically conductive layer 160having conductive particles 162 distributed in a suspension material 164is formed on the test substrate 102 and contact pads 104.

The anisotropically conductive layer 160 is formed such that electricalresistance in one direction through the layer 160 differs from thatmeasured in the other directions. Typically, electrical conductivity isprovided in one direction (e.g. the “z” direction) while high resistanceis provided in all other directions. The conductivity in the onedirection may be pressure sensitive, requiring that the material becompressed in that direction to achieve the desired conductivity.

One type of anisotropically conductive material suitable for forming theanisotropically conductive layer 160 is known as a “z-axis anisotropicadhesive.” In the z-axis anisotropic adhesive, the conductive particles162 are distributed to a low level such that the particles do notcontact each other in the xy plane. Compression of the layer 160 in thez direction, however, causes the conductive particles 162 to contacteach other in the z direction, establishing an electrically conductivepath. The conductive particles 162 may be formed from any suitableelectrically conductive materials, such as gold, silver, or otherelectrically conductive elements or compounds. Similarly, the suspensionmaterial 164 may be include, for example, a thermoset polymer, a B-stage(or “pre-preg”) polymer, a pre-B stage polymer, a thermoplastic polymer,or any monomer, polymer, or other suitable material that can support theelectrically conductive particles 162.

Z-axis anisotropic adhesives may be formed in a number of ways,including, for example, as a film or as a viscous paste that is applied(e.g. stenciled, sprayed, flowed, etc.) to the contact pads 104. Theanisotropically conductive adhesives may then be cured. Curing may beperformed in a variety of ways, such as by subjecting the materials tocertain environmental conditions (e.g. temperature, pressure, etc.), orby the removal of solvents or suitable curing compounds, or byirradiation/exposure to ultraviolet or ultrasonic energy, or by othersuitable means.

For example, z-axis anisotropic adhesives are commercially available inboth a thermoplastic variety or a thermosetting variety. Thermoplasticanisotropic adhesives are those that are heated to soften forapplication to the test substrate and then cooled for curing, andinclude, for example, solvent-based hot-melt glue. Conversely,thermosetting anisotropic adhesives are suitable for application to thetest substrate at normal ambient temperatures, and are heated for curingat temperatures from 100° C. to 300° C. for periods from several minutesto an hour or more. Suitable z-axis anisotropic adhesives include thoseavailable from A.I. Technology, Inc. of Trenton, N.J., or Sheldahl, Inc.of Northfield, Minnesota, or 3M of St. Paul, Minn.

As best seen in FIG. 4, the anisotropically conductive layer 160 isformed on the test substrate 102, and the bumped die 10 is positionedadjacent to the layer 160 with the solder (or conductive) bumps 16approximately aligned with the contact pads 104. The bumps 16 mayalternately be formed of any suitable, electrically conductive material.For bumped die 10 having solder bump pitches of at least 32 μm,conventional mechanical alignment devices may be used. For finerpitches, however, more advanced optical alignment systems may benecessary, such as the type of alignment apparatus shown and describedin U.S. Pat. No. 4,899,921 to Bendat et. al., incorporated herein byreference.

In the test carrier 100, the solder bumps 16 are compressed into theanisotropically conductive layer 160 prior to the curing of the layer160 so that the solder bumps 16 become embedded in the layer 160. Thecompression of the solder bumps 16 into the anisotropically conductivelayer 160 compresses the conductive particles 162 into contact with eachother and creates an electrically conductive path 166 between each ofthe solder bumps 16 and its corresponding contact pad 104.

In the test carrier 100, the solder bumps 16 become attached to the testcarrier 100 during the curing of the anisotropically conductive layer160. For example, in one embodiment, an anisotropically conductive layer160 having a B stage polymer as the suspension material 164 is appliedto the test carrier 100. A bumped die 10 is pressed into the layer 160until the solder bumps 16 are “tacked” in position, and then the bumpeddie 10 and test carrier 100 are placed in an oven and heated to 150° C.At this temperature, the polymer is fully cross-linked, curing the layer160 to a hardened consistency.

One or more test signals are then transmitted to the bumped die 10through one or more of the test leads 106, through the contact pads 104,across the conductive paths 166, through the solder bumps 16, and intothe bumped die 10. Output signals from the bumped die 10 are thencommunicated from the solder bumps 16 back across the conductive paths166 to the contact pads 104 and other test leads 106, and are monitoredto determine whether the bumped die 10 is functioning to the desiredspecifications.

After testing, the bumped die 10 may be removed from the test carrier100 by detaching the solder bumps 16 from the anisotropically conductivelayer 160. This may be accomplished in a number of ways depending uponthe properties of the anisotropically conductive layer 160, including,for example, by heating the layer 160 until it softens, or by applyingsolvents to dissolve the layer, or by other suitable means. After thebumped die 10 is removed, the test carrier 100 may be used to testanother bumped die 10.

Alternately, FIG. 4 may represent a cross-sectional view of the bumpeddie 10 attached to any electronic component, such as a printed circuitboard 100. In that case, the bumped die 10 may be aligned with thecontact pads 104 and attached with the anisotropically conductive layer160 as described above, except that the bumped die 10 is not removed andremains secured to the printed circuit board 100.

Although the anisotropically conductive layer 160 is shown in FIG. 4 asbeing a single, continuous layer covering the entire test substrate 102,it is not necessary that only one layer be used, or that the layer becontinuous. Rather, the anisotropically conductive material may beformed on a plurality of contact pads 104 of the test carrier (orprinted circuit board) 100 in a variety of patterns, including, forexample, in strips covering rows of contact pads, or in a checkerboardpattern covering regions of contact pads.

Furthermore, it is not necessary that the anisotropically conductivelayer 160 be formed on the test carrier (or printed circuit board) 100,but rather, the layer 160 might be formed on the solder bumps 16 of thebumped die 10. After the layer 160 is applied to the solder bumps 16,the test carrier 100 may be engaged with the layer to form the desiredelectrical connections for testing of the die.

The anisotropically conductive layer 160 advantageously improves theprocess of testing and assembling of bumped die 10 and other bumpeddevices. The process of attaching (and detaching) the bumped die 10 tothe test carrier (or printed circuit board) 100 using theanisotropically conductive layer 160 may be less time consuming and moreeconomical than the prior art process of soldering (and unsoldering) thesolder bumps 16 to (and from) the contact pads 104 because the reworktemperatures of the anisotropically conductive layer 160 (typically 80°C. to 150° C.) may be less than the typical reflow temperature of solder(183° C.). Thus, less time and energy may be needed to bring thetemperatures of the bumped die 10 and test carrier 100 up to thetemperature necessary for detachment, and the potential for damaging thesolder bumps 16 or the contact pads 104 may be decreased due to thereduced rework temperatures.

Another advantage of the test carrier (or printed circuit board) 100having the anisotropically conductive layer 160 is that a more flexibleconnection may be provided between the solder bumps 16 and the contactpads 22 than is obtained using solder. If the bumped die 10 and testcarrier 100 are subjected to a large range of temperatures or repeatedlythermal cycling during the testing (e.g. burn-in tests), the flexibilityof the layer 160 may relieve stresses that might otherwise occur due tothe differences in the CTE of the bumped die 10 and the test carrier100. Depending upon the anisotropically conductive materials used, theanisotropically conductive layer 160 may advantageously expand andcontract during such testing to prevent delamination or other damage tothe bumped die 16 or the test carrier 100, or to prevent damage fromoccurring at the connection between the solder bumps 16 and the bondpads 14.

An additional advantage of the anisotropically conductive layer 160 isthat satisfactory electrical contact may be achieved between the contactpads 104 and the solder bumps 16 despite the variation in the heights ofthe solder bumps 16. Because the tallest solder bumps 16 become embeddedin the layer 160, if the layer 160 is properly sized, even the shortestsolder bumps 16 may be brought into contact with the layer 160 to forman electrical path 166 between the solder bumps 16 and the contact pads104. The anisotropically conductive layer 160 may therefore improve theelectrical connection between the short solder bumps and the contactpads.

The anisotropically conductive layer 160 may also reduce the compressionforce needed to bring the short solder bumps 16 into electrical contactwith the contact pads 104. Because the compression force is reduced, thepotential for damaging the bumped die 10 or the test carrier (or printedcircuit board) 100 is reduced.

Yet another advantage of the anisotropically conductive layer 160 isthat the solder bumps 16 of the bumped die 10 may be easily cleaned ofany residual amounts of the anisotropically conductive materialfollowing testing. Some anisotropically conductive materials arecommercially available that are readily dissolvable using solvents forease of removal and cleanup. One solvent that may be suitable (dependingupon the anisotropically conductive material used) is RS 816 availablefrom AI Technology, Inc. of Princeton, N.J. Thus, the time consumingtask of flux cleaning associated with traditional soldering may beavoided.

FIG. 5 is a partial cross-sectional view of the bumped die 10 of FIG. 1engaged with a test carrier 100 b in accordance with an alternateembodiment of the invention. In this embodiment, the test carrier 100 bincludes an anisotropically conductive layer 160 b that has a flexibleouter surface 168. The flexible outer surface 168 may be formed, forexample, by at least partially curing the anisotropically conductivelayer 160 b prior to engagement with the bumped die 10. The flexibleouter surface 168 may be a resilient surface.

To test the bumped die 10 using the test carrier 100 b, the die ispositioned over the layer 160 b with the solder bumps 16 approximatelyaligned with the contact pads 104. The solder bumps 16 are thencompressed against the flexible outer surface 168 causing localizedcompression of the anisotropically conductive material 160 b in theregion near each of the solder bumps 16. The conductive particles 162are brought into contact by the compression forces to form theconductive paths 166 between each of the solder bumps 16 and thecorresponding contact pads 104. Test signals are then transmitted to thebumped die 10 through some of the test leads 104 and the conductivepaths 166, and output signals from the bumped die 10 are transmittedfrom the solder bumps 16 through the conductive paths 166 to the testcarrier 100 b as previously described above.

After the bumped die 10 has been tested, it is disengaged from the testcarrier 100 b by simply moving the solder bumps 16 away from theflexible outer surface 168 of the anisotropically conductive layer 160b. If the flexible outer surface 168 of the layer 160 b is a resilientsurface, the localized compression areas near each of the solder bumps16 will spring back to their uncompressed shape.

The test carrier 100 b having the layer 160 b with the flexible outersurface 168 may further improve the process of testing of the bumped die10 by reducing or eliminating the time and effort involved in detachingthe solder bumps 16 from the anisotropically conductive layer 160 b.Because the solder bumps 16 are not embedded in the layer 160 b, it isnot necessary to reheat the bumped die 10 or the test carrier 100 b tothe rework temperature of the anisotropically conductive layer 160 b inorder to disengage the die from the test carrier. The time, effort, andexpense associated with disengaging the solder bumps 16 from theanisotropically conductive layer 160 may therefore be reduced oreliminated.

Similarly, because the solder bumps 16 are not embedded in theanisotropically conductive layer 160 b, the time, effort, and expenseassociated with cleanup of any residual anisotropically conductivematerial deposited on the solder bumps 16 may also be reduced oreliminated. Depending upon the anisotropically conductive material used,the transfer of material to the solder bumps 16 may be minimized oreliminated so that the solder bumps 16 may be clean enough for immediateuse after testing.

FIG. 6 is a partial cross-sectional view of the bumped die 10 engagedwith a test carrier (or printed circuit board) 200 in accordance withanother alternate embodiment of the invention. In this embodiment, thetest carrier 200 includes a test substrate 202 having a plurality ofpockets 244 disposed therein. A plurality of test leads 206 are formedon the test substrate 202, each test lead 206 terminating in a contactpad 204 that is formed within each of the pockets 244. Ananisotropically conductive layer 260 is formed on the test substrate (orprinted circuit board) 202 covering the contact pads 204 and test leads206. The anisotropically conductive layer 260 includes a plurality ofconductive particles 262 contained with a suspension medium 264, and anouter surface 268.

In operation, the solder bumps 16 of the bumped die 10 are at leastpartially disposed within the pockets 244 of the test carrier 200. Thesolder bumps 16 may be embedded in the anisotropically conductive layer260 prior to the curing of the layer, or alternately, the layer 260 maybe at least partially cured so that the outer surface 268 is a flexiblesurface and the solder bumps 16 do not penetrate the outer surface 268or become attached to the layer 260. In either case, a compression forcemay be applied to the bumped die 10 (or to the test carrier 200) tocompress the anisotropically conductive material to form a conductivepath 266 between each solder bump 16 and each contact pad 204. Testingmay then be performed on the bumped die 10. After testing is complete,the bumped die 10 may be disengaged from the test carrier 200 in one ofthe ways described above. Alternately, in the case of the bumped die 10being attached to the printed circuit board 200, the bumped die 10 isnot disengaged.

The test carrier 200 having the pockets 244 and the anisotropicallyconductive layer 260 further improves the testing of the bumped die 10by providing the desired electrical contact between the solder bumps 16and the contact pads 204 without penetration of the solder bumps 16using contact blades 48 or the like (see FIG. 2). Despite thevariability of the size and shape of the solder bumps 16, theanisotropically conductive layer 260 provides the necessary electricalcontact along the conductive paths 266 between the solder bumps 16 andthe contact pads 104. Because the contact blades 48 may be eliminated,fabrication and maintenance of the test carrier 200 is simplifiedcompared to the prior art test carrier 40 shown in FIG. 2. Also, thepotential for the solder bumps 16 to be cracked, chipped, or otherwisedamaged due to penetration by the contact blades 48 is eliminated.

Similarly, when the bumped die 10 is engaged with the printed circuitboard 200 having pockets 244 and the anisotropically conductive layer260, the electrical contact between the bumps 16 and the contact pads204 is improved. As shown in FIG. 6, electrical contact between thesolder bumps 16 and the sidewalls 204 is achievable over a largercontact area due to the anisotropically conductive layer 260, providingimproved electrical contact compared with the contact blades 48 of theprior art device (FIG. 2). Also, because the contact blades 48 may beeliminated, the manufacturing the pockets 244 is simplified. The pockets244 may be formed, for example, by masking the areas surrounding thelocations of the pockets 244 with a hard mask, and then etching thesubstrate using an etchant (e.g. KOH).

FIG. 7 is a partial cross-sectional view of the bumped die 10 engagedwith a test carrier (or printed circuit board) 300 in accordance withyet another embodiment of the invention. In this embodiment, the testcarrier 300 includes a test substrate 302 having a plurality ofpedestals 364 projecting upwardly therefrom. Test leads 306 are formedon the test substrate 302, each test lead 306 terminating in a contactpad 304 formed on at the top of each pedestal 364.

A magnet 380 having a north pole 382 and a south pole 384 is positionednear the test substrate 302. A plurality of magnetic flux lines 386(only two shown in FIG. 7) emanate from the magnet 380. Ananisotropically conductive layer 360 having a plurality of conductiveparticles 362 and an outer surface 368 is formed on the test substrate302. An optical alignment system 390 (such as the type of alignmentapparatus shown and described in U.S. Pat. No. 4,899,921 to Bendat et.al.) is positioned proximate the solder bumps 16 to ensure the alignmentof the solder bumps 16 with the contact pads 304. A die handler 392 isengaged with and controllably positions the bumped die 10. Numeroustypes of die handlers 392 are suitable for this purpose, including, forexample, those shown and described in U.S. Pat. No. 5,184,068 to Twigget. al., U.S. Pat. No. 5,828,223 to Rabkin et. al., and the IC handlersavailable from Verilogic Corporation of Denver, Colo.

During the formation of the anisotropically conductive layer 360, theconductive particles 362 align with the magnetic flux lines 386 to formconductive columns along the flux lines which form a conductive path 366between each solder bump and its corresponding contact pad. If themagnetic flux lines 386 are strong enough, some of the conductiveparticles 362 may be induced to protrude from the surface 368 of thelayer 360 (as shown in FIG. 7). Suitable anisotropically conductivematerials that form conductive paths 366 when exposed to a magneticfield include, for example, the Elastomeric Conductive PolymerInterconnect (ECPI) materials available from AT&T Bell Laboratories ofMurray Hill, New Jersey. For testing of the bumped die 10, the solderbumps 16 may either be embedded in the anisotropically conductive layer360 prior to the curing of the layer, or alternately, the layer 360 maybe at least partially cured so that an outer surface is a flexiblesurface that is not penetrated by the solder bumps 16. In either case,the solder bumps 16 are engaged with the anisotropically conductivelayer 360 using the die handler 392 and the optical alignment system 390so that each of the solder bumps 16 are electrically coupled to acorresponding one of the contacts pads 304 by at least one of theconductive paths 366. Testing may then be performed on the bumped die10, and the bumped die 10 may be disengaged from the test carrier 300 inone of the ways described above.

An advantage of the test carrier 300 having the pedestals 364 and theanisotropically conductive layer 360 is that the desired electricalcontact between the solder bumps 16 and the contact pads 304 is providedwithout penetration of the solder bumps 16 using the projections 69 (seeFIG. 3). Because the projections 69 may be eliminated, fabrication ofthe test carrier (or printed circuit board) 300 is simplified comparedto the prior art test carrier 60 shown in FIG. 3. Also, the potentialfor the solder bumps 16 to be cracked, chipped, or otherwise damaged dueto penetration by the projections 69 is eliminated.

Another advantage is that the bumped device 10 may be engaged with thetest carrier 300, tested, and disengaged rapidly and efficiently. Theanisotropically conductive layer 360 eliminates the time and expenseassociated with reflowing the solder bumps 16, and provides the desiredelectrical contact despite variation in the heights of the solder bumps16.

Although the above described embodiments of the anisotropicallyconductive layers have been described with specific reference toanisotropically conductive materials that form electrically conductivepaths when subjected to a compression force, some anisotropicallyconductive materials do not require a compression force to formconductive paths. For such materials, the desired electrical contactbetween the solder bumps and the contact pads of the test carrier may beformed without applying a compression force.

Suitable anisotropically conductive materials that do not require acompression force to form conductive paths include, for example,Elastomeric Conductive Polymer Interconnect (ECPI) materials availablefrom AT&T Bell Laboratories of Murray Hill, N.J. Conductive paths areformed in AT&T Bell's ECPI materials by subjecting the materials to amagnetic field.

The detailed descriptions of the above embodiments are not exhaustivedescriptions of all embodiments contemplated by the inventors to bewithin the scope of the invention. Indeed, persons skilled in the artwill recognize that certain elements of the above-described embodimentsmay variously be combined or eliminated to create further embodiments,and such further embodiments fall within the scope and teachings of theinvention. It will also be apparent to those of ordinary skill in theart that the above-described embodiments may be combined in whole or inpart with prior art apparatus and methods to create additionalembodiments within the scope and teachings of the invention.

Thus, although specific embodiments of, and examples for, the inventionare described herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. The teachings providedherein of the invention can be applied to other apparatus and methods oftesting and assembling bumped devices using anisotropically conductivelayers, and not just to the apparatus and methods described above andshown in the figures. In general, in the following claims, the termsused should not be construed to limit the invention to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all apparatus and methods of testing and assemblingbumped devices using anisotropically conductive layers that operatewithin the broad scope of the claims. Accordingly, the invention is notlimited by the foregoing disclosure, but instead its scope is to bedetermined by the following claims.

What is claimed is:
 1. A semiconductor device, comprising: a bumpeddevice having a plurality of conductive bumps formed thereon; asubstrate having a plurality of substantially flat contact padsdistributed thereon and approximately aligned with the plurality ofconductive bumps; and an anisotropically conductive layer disposedbetween the bumped device and the substrate and mechanically coupled tothe substrate, the anisotropically conductive layer having a flexibleouter surface in contact with the plurality of conductive bumps, theconductive bumps not being embedded within the anisotropicallyconductive layer, the conductive bumps compressing the flexible outersurface without penetrating the flexible outer surface to form acompression area at each of the conductive bumps and to electricallycouple each of the conductive bumps with a corresponding one of thecontact pads.
 2. The semiconductor device of claim 1 wherein the bumpeddevice comprises a bumped die having a plurality of solder bumps formedthereon.
 3. The semiconductor device of claim 1 wherein theanisotropically conductive layer comprises a thermosettinganisotropically conductive adhesive.
 4. The semiconductor device ofclaim 1 wherein the anisotropically conductive layer comprises athermoplastic anisotropically conductive adhesive.
 5. The semiconductordevice of claim 1 wherein the anisotropically conductive layer comprisesa suspension material having a plurality of conductive particles.
 6. Thesemiconductor device of claim 5 wherein at least some of the conductiveparticles are engaged into contact to form a conductive path betweeneach conductive bump and the corresponding one contact pad.
 7. Anapparatus for testing a bumped device having a plurality of conductivebumps, comprising: a substrate including a first surface having aplurality of substantially flat contact pads distributed thereon, thecontact pads being substantially alignable with the plurality ofconductive bumps; and an anisotropically conductive layer disposed onthe first surface and having a flexible outer surface engageable withthe plurality of conductive bumps, the conductive bumps not beingembedded within the flexible outer surface, the conductive bumpscompressing the flexible outer surface without penetrating the flexibleouter surface to form a compression area at each of the conductive bumpsand to electrically couple each of the conductive bumps with acorresponding one of the contact pads.
 8. The apparatus of claim 7wherein the flexible outer surface comprises a resilient outer surfaceengageable with the plurality of conductive bumps.
 9. The apparatus ofclaim 7 wherein the anisotropically conductive layer comprises ananisotropically conductive paste.
 10. The apparatus of claim 7, furthercomprising an alignment device engageable with the bumped device toapproximately align the conductive bumps with the contact pads.
 11. Theapparatus of claim 10 wherein the alignment device comprises an opticalalignment device.
 12. The apparatus of claim 7, further comprising abumped device handler engageable with the bumped device for controllablypositioning the bumped device into engagement with the anisotropicallyconductive layer.
 13. The semiconductor device of claim 1 wherein theflexible outer surface comprises a resilient outer surface.